1. Field of the Invention
The present invention relates to a plate supplying apparatus, and more particularly to a plate supplying apparatus for supplying a plate from a storage section where plates are stored, while reversing its faces.
2. Related Art Statement
A conventional plate supplying apparatus automatically supplies a plate, such as a presensitized (PS) plate, to an image recording apparatus for irradiating that plate with a laser beam to directly record an image thereon. The plate used with such an image recording apparatus is made up of a support layer and an image recording layer. Since the image recording layer is easily damaged, the utmost caution is required when taking out the plate.
The conventional plate supplying apparatus receives a cassette storing a plurality of plates. In the cassette, a slip sheet for preventing friction between plates may be provided between plates. However, in order to achieve efficient storing of plates into a cassette and to simplify the mechanism of a plate supplying apparatus, the use of the slip sheet may be abolished and only plates may be stored. For example, Japanese Patent Laid-Open Publication No. 8-242340 discloses a plate supplying apparatus which includes, for example, pad rods having plate suction cups. In the state where the plate suction cups secure a support layer side of a plate via suction, the pad rods move the plate suction cups to a predetermined position, so that the plate is taken out from a cassette, and then supplied to an image recording apparatus as described above.
Referring to FIGS. 17 and 18, the operation of the above-described conventional plate supplying apparatus 500 is described. FIG. 17 is a schematic view illustrating the construction of the plate supplying apparatus 500 and an image recording apparatus 600, and FIG. 18 is a view used for explaining a reference path for transporting a plate P.
In FIG. 17, a plurality of plates P to be supplied from the plate supplying apparatus 500 are stored in a cassette 510 placed in a slanting position, such that the support layer faces the side of a plate transport mechanism 520. The plate transport mechanism 520 transports the plates P from the cassette 510 to the image recording apparatus 600. The plate transport mechanism 520 includes a traveling member 524 which travels by receiving drive from an endless synchronous belt 522 looped over two pulleys 521a and 521b which are caused to pivot by drive of a motor M523. The traveling member 524 has an arm 526 secured thereon. At an end of the arm 526, there are provided a plurality of suction pads 525 for holding the plate P via suction. The suction pads 525 are provided so as to be in a proper position with respect to the plates P stored in the cassette 510.
In the case where the plate transport mechanism 520 having the above-described construction is in a state A where the motor M523 drives the synchronous belt 522 in a counterclockwise direction, whereby the traveling member 524 takes out a plate P stored in the cassette 510, when the traveling member 524 moves toward a direction to the left (hereinafter referred to as the “linear motion direction”), the arm 526 and the suction pads 525 pivot in a counterclockwise direction (hereinafter, referred to as the “transport rotation direction”). Therefore, in the case where the suction pads 525 hold a support layer side of a plate P via suction in state A, and then the traveling member 524 is moved by drive of the motor M523 toward the linear motion direction, when the arm 526 and the suction pads 525 pivot in the transport rotation direction, the plate P held via suction by the suction pads 525 is turned such that the plate's faces are reversed (i.e., the support layer of the plate P faces downwards). Thereafter, the plate P is transported to a transport unit 620 included in the image recording apparatus 600. Note that the angle of rotation in the transport rotation direction with respect to the movement in the linear motion direction is uniquely fixed. Then, the transport unit 620 transports the plate P having been turned and transported by the plate transport mechanism 520, to a recording drum 610. In the recording drum 610, the plate P is secured.
Another exemplary pivot system in the plate transport mechanism 520 may be such that the traveling member 524 includes a reduction gear (not shown) having a pinion to be engaged with a rack rail (not shown) provided in parallel with the synchronous belt 522, and the reduction gear has the arm 526 secured on an output shaft thereof. In this construction, when the traveling member 524 moves in the linear motion direction, the pinion is engaged with the rack rail and rotated, whereby the output shaft of the reduction gear also rotates at a predetermined deceleration. Accordingly, the arm 526 secured on the output shaft of the reduction gear and the suction pads 525 also pivot about the center of the output shaft of the reduction gear at a predetermined deceleration in the transport rotation direction. Note that the angle of rotation in the transport rotation direction with respect to the movement in the linear motion direction can be adjusted to any value by changing the deceleration, but once adjusted, the angle of rotation is uniquely fixed.
Next, referring to FIG. 18, the angle in the transport rotation direction of a plate P with respect to the movement in the linear motion direction is described. As described above, the image recording layer of a plate P is easily damaged, and thus, friction between a plate P taken out from the cassette 510 and another plate P which remains stored in the cassette 510 needs to be prevented. For this purpose, the plate to be transported will attain an optimum path if the upper end of the plate to be transported follows a line slightly below a “reference path”, where the reference path is defined as an arc of a circle whose radius is the length of a plate stored in the cassette 510 and whose center is the lower end of the plate. If the upper end of the plate follows a line above the reference path, the plate P will be dragged upwards, thus causing friction between the plate P being transported and another plate in the cassette 510. On the other hand, if the upper end of the plate follows a line too far below the reference path, a reaction force that causes the plate P to return to its flat state may exceed the suction force of the suction pads 525, and cause the suction pads 525 to be detached from the plate P, especially when taking out a plate P with high flexibility (stiffness) from the cassette 510.
Now, the case of transporting a plate P1, shown in FIG. 18, is described. For simplicity of description, it is conveniently assumed that the “optimum path” is attained if the upper end of a plate P to be transported just follows the reference path. The plate P1 with length L1 is taken out from the cassette 510 by the plate transport mechanism 520 such that the upper end of the plate P1 follows an arc R1. The suction pads 525 suck the upper end of the plate P1 stored in the cassette 510 at a point e0 (i.e., at the position of the suction pads 525 in the above-described state A). Although the illustration of FIG. 18 is simplified so that the suction pads 525 appear to be sucking at the upper end of the plate P1, the suction pads 525 will suck somewhat below the upper end in practice. It is further assumed that the pivotal point of the arm 526 when the suction pads 525 are situated at the point e0 is S0, and that the arm 526 constitutes an angle of θ0 with respect to the horizontal direction. In order to prevent friction between the plate P1 to be taken out and another plate P1 stored in the cassette 510, the plate P1 to be taken out needs to be removed from the cassette 510 without allowing a lower end f1 thereof to be displaced with respect to the plate P1 stored in the cassette 510. That is, the reference path should be such that the suction pads 525 travel from the point e0 to a midpoint e1 along the arc R1 having the radius L1 and a center at the lower end f1.
As described above, the angle of rotation in the transport rotation direction, as a function of the movement in the linear motion direction, is uniquely fixed. In the plate transport mechanism 520, this presents a difficulty in transporting plates P having different lengths, for example, while preventing the above-described friction and large bending stress.
For example, in FIG. 18, in the case of a plate P1 with length L1, the arm 526, when the suction pads 525 are situated at the transport midpoint e1, has a pivotal point of S1 and an angle θ1 with respect to the horizontal direction. As the plate P1 is transported, the suction pads 525 move along the path of the arc R1, which is the reference path. However, the following problem arises when the same plate transport mechanism 520 is used to transport a plate P2 with length L2 which is greater than the length L1 (in FIG. 18, the plate P2 is indicated by a broken line to distinguish it from the plate P1).
The suction pads 525 will start to suck the plate P2 stored in the cassette 510 at the point e0, which is the same as that for the plate P1. The arm 526, when the suction pads 525 are situated at the point e0, has a pivotal point of S0 and an angle θ0 with respect to the horizontal direction. The reference path should be such that the plate P2 is transported along the arc R2 having the radius L2 and a center at the lower end f2. Thus, the reference path for transporting the plate P1 is different from that for transporting the plate P2. Specifically, in the case where the plate P2 with the length L2 is transported, the arm 526 constitutes an angle of θ2 with respect to the horizontal direction when the suction pads 525 are situated at the midpoint e2. That is, in the case of transporting the plate P2, the degree of change in the angle of rotation in the transport rotation direction as a function of the amount of movement in the linear motion direction needs to be made greater than that in the case of transporting the plate P1. For example, if the plate P1 is transported by setting the angle of rotation according to the plate P2, the plate P1 will be damaged due to the friction between the plate P1 and another plate, etc. On the other hand, if the plate P2 is transported by setting the angle of rotation according to the plate P1, an unwanted bending pressure will be applied to the plate P2, and as a result, the suction pads 525 may be detached from the plate P2 because of the flexibility (stiffness) of the plate P2.
As described above, since the reference path for transporting a plate varies depending on the length of a plate P to be transported, if the angle of rotation in the transport rotation direction with respect to the movement in the linear motion direction is uniquely fixed, it is difficult to support various paths. In addition, the above-described “optimum path” may also vary with factors such as changes in the remaining number of plates P stored in the cassette 510, differences in the thickness of plates P to be transported, and differences in the flexibility (stiffness) of plates P. Thus, what is needed is an ability to support various “optimum paths” while taking into account various factors.